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Topic: using LCD numeric displays without controller (Read 3059 times) previous topic - next topic

Lsnyman

I have been trying to find a tutorial or discussion on using Numeric LCD displays that do not have a built-in controller. These are the 3.5 digit types that look like a Dip.
Is there a way to use these with Arduino or do you have to install a controller for it?
Sorry if this covered elsewhere.

johnwasser

You certainly need something to drive the display.  First thing to check is the number of pins you have to drive.  Let's use for an example the Lumex LCD-S3X1C50TF/A.

http://www.mouser.com/ds/2/244/LCD-S3X1C50TF%20A-97526.pdf

There are 40 pins but two go to Common and eight are N/C so that leaves 31 you have to drive (23 if you only want digits and not decimal points, colon +/-, Overflow, LoBat).  That's a little too many for the Arduino UNO which only has 20 pins.  The Arduino MEGA could drive it.  There is an article somewhere on the Atmel site that says how to drive an LCD directly from ATmega pins.
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dhenry

Quote
I have been trying to find a tutorial or discussion on using Numeric LCD displays that do not have a built-in controller.


They can be fairly involved to drive, especially those with 1/4 or less duty cycles.

You may want to start with static ones (1 com, or 1/2 duty cycle). 1/3 is manageable (you can generate the bias via a resistor network), but more than that, you want to use a chip with dedicated lcd controllers - atmel makes some.

The key is that the segments with polarity opposite that of the com goes black, and segments with polarity the same as the com's are invisible. com needs to flip constantly, but typically no faster than 100hz: too fast, you face ghosting; too slow, you face fading.

It is a bitch to drive. But incredibly low power consumption and nice visibility.

johnwasser

The document is Application Note AVR340: Direct Driving of LCD Using General Purpose IO

http://www.atmel.com/Images/doc8103.pdf

The example uses an ATmega48 and the Pacific Display PD-332 Multiplexed 3 1/2 Digit Liquid Crystal Display.

"The LCD described within is Glass-only device (no interface IC on the LCD). The LCD has 4 COM inputs and 8 segment inputs, requiring 12 I/Os on the ATmega48. There are 11 to 16 additional I/Os still available on the ATmega48, depending on the package chosen."
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Lsnyman

Thank you very much for the advice. It seems like it is much easier to stick with the units that have a driver. The reasson I was looking at changing is i am trying to save space from the Bulky 8x2 display I am using now. I dont really need a baclight and i could do what I need with just 3 1/2 characters. Does anyone know of a compact lcd without the big metal frame and backlight that has a driver chip on board?

johnwasser

Can't find anything at DigiKey.com to match your specs.  You may need to buy the driver separately like the Microchip AY0438/P, a 40-pin DIP containing 32 LCD segment drivers.
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dhenry

There are some COG hd44780 compatible displays. But most of them come with ribbon cables.

MarkT

Also if you drive an LCD and don't ensure each segment gets zero DC bias you can slowly destroy the segments
via electrolysis (or something like that).  Driver chip saves a lot pins and work - but you might enjoy getting
it working the hard way!
[ I won't respond to messages, use the forum please ]

karbombsie

Hi All,

I had a similar issue. I'm looking to use the following LCD screen with my Arduino Mega 2560 (http://www.mouser.com/ProductDetail/Lumex/LCD-S401C39TF/?qs=FxUKTwyvCu6h5PZfX8iZtw==). Are all driver IC's going to be compatible with this and the arduino? If not, what is it that I should be watching out for?

Thanks.

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